Fiberboard panels can provide aesthetic appeal, acoustical modification or dampening, accessibility to space above the ceiling plane, and simple installation and removal. To accommodate these features at a relatively low cost, panels are constructed using strong but relatively inexpensive panel-forming materials, such as mineral fiber, cellulosic fiber, perlite and binder.
Two of several fiberboard performance properties sought to be optimized are acoustical resistivity and board hardness. Those skilled in the art will appreciate that most conventional attempts to optimize one or both of these performance properties, including modifying the formulation of the panel and/or the process for producing the panel, resulted in improved performance of one characteristic and a reduction in the performance of the other.
The wet-felting process is a known process for fabricating acoustical panels. In the wet-felting process, an aqueous slurry of the panel-forming materials is deposited onto a moving wire screen, such as a fourdrinier or cylinder former. On the wire screen of a fourdrinier, a wet mat is formed by dewatering the aqueous slurry by gravity and then optionally by vacuum suction. The wet mat is pressed to a desired thickness between press rolls and the wire screen for additional dewatering. The pressed mat is dried in ovens or kilns and then cut to produce acoustical panels. However, the combination of low level resistivity and high level board hardness has not been achieved in single layer fiberboards produced using conventional wet-felting technology.
One known way to obtain the aforementioned combination of performance properties via the wet-felting process is to use overlays having nodulated mineral fibers. Wet-formed panels having nodulated mineral fiber overlays, are described in U.S. patent application Ser. No. 09/860,271. The disadvantages of the overlay technology are the high capital cost necessary to produce and adhere the overlay and the overall increased process complexity.
The aforementioned performance properties can also be achieved in fiberboard panels using the well know cast process. In the cast process, a mixture of mineral fiber, cellulosic fiber, perlite, binder and other board-forming ingredients are deposited on trays which have been covered with paper or foil. The filled trays are typically placed in an oven in order to dry the mixture. The dried sheets are typically surface treated to obtain a desired thickness and are cut into panels. One of the disadvantages of using the cast technology to achieve the desired performance properties is the high cost to produce the panels which results from the slow production rate.